Rationale and Objectives:We have developed a new contrast enhancement protocol for subtraction coronary computed tomography (SCCTA) requiring a short breath-holding time. In the protocol, test and main boluses were sequentially and automatically injected, and correct timings for pre-contrast and contrast-enhanced scans for main bolus were automatically determined only by the test bolus tracking. Combined with a fixed short main bolus injection for 7 seconds, the breath-holding time was shortened as possible. The purpose of this study was to evaluate whether use of this new protocol produced adequate quality images, taking into account calcified lesions and in-stent lumens.Materials and Methods: Patients (n = 127) with calcium scores of >400 Agatston units or a history of stent placement were enrolled. Breath-holding times were recorded, and image quality was visually evaluated by two observers.Results: The mean ± standard deviation breath-holding time was 13.2 ± 0.6 seconds. The mean ± SD computed tomography (CT) number of coronary arteries for the pre-contrast scan was sufficiently low [99.2 ± 32.2 Hounsfield units (HU)] and, simultaneously, that for SCCTA was 367.0 ± 77.2 HU. The rate of segments evaluated as unreadable was sufficiently low (3.8%).Conclusions: Use of the SCCTA protocol was efficient and allowed for a shorter breath-holding time and adequate diagnostic accuracy of SCCTA images, including images of calcified and stent implantation segments.

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Coronary CTA provides good visualization of collaterals used in retrograde CTO PCI. For retrograde guidewire crossing, a higher success rate with fewer complications was observed in CTA-visible collaterals than in those not detectable in coronary CTA.

A 50-year-old man with a history of smoking and hyperlipidemia, but no chest pain, was admitted because of an abnormal electrocardiogram and regional wall motion abnormality on echocardiography (mild inferior hypokinesis). Coronary angiography revealed 2 chronic total occlusions (CTOs): ostial right coronary artery (RCA) and mid left circumflex artery. C A B Figure 1. Baseline Coronary Angiogram and Subintimal Wiring (A) An extremely long chronic total occlusion (CTO) from the ostium of the right coronary artery (RCA) to the distal bifurcation (arrowheads) was seen in the pre-interventional angiogram. The contralateral injection showed an epicardial collateral from left anterior descending coronary artery to the RCA. (B) The CTO was successfully crossed using a retrograde approach via this epicardial collateral combined with the intentional creation of subintimal lumen using a stiff guidewire. Coronary angiography showed a large coronary dissection in the proximal RCA. (C) The intravascular ultrasound catheter (white arrow in B) was placed in the subintimal space, and the true lumen was collapsed at the 2-o'clock position.

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